Microscopic imaging apparatus and method

ABSTRACT

A handheld confocal imaging system for in vivo observation of dermal and subdermal tissue allows diagnosis of conditions substantially beneath the surface of the skin. A confocal head has optics which scan the tissue so as to provide images of vertical sections of the tissue. Both two and three dimensional imaging may be provided for diagnosis and location of basal cell carcinomas and melanomas, and so as to enable visualization of tumor borders prior to excision.

This application claims the priority benefit of co-pending provisionalapplication, Ser. No. 60/001,141, filed Jul. 13, 1995.

FIELD OF THE INVENTION

The present invention relates to handheld confocal imaging system for invivo clinical examinations of dermal and subdermal tissues usingnon-ionizing radiation, and particularly laser radiation which is of awavelength capable of penetrating into the skin.

The invention is especially suitable for providing an instrument fordermal pathology applications. The invention is also applicable forvisualizing sections in other scattering media than tissue. Theinvention enables the use of a laser as a source of illumination. Theinstrument may provide data to image processing computers, which may beprogrammed to provide high resolution images of dermal sections.

BACKGROUND OF THE INVENTION

Systems have been proposed for viewing the surface areas of the skin orthe external surfaces of internal tissue. Viewing without scanning isdescribed in Pennypacker, U.S. Pat. No. 4,817,622, issued Apr. 4, 1989.Examination of internal tissue surfaces by means of beam scanning areproposed in Harris, U.S. Pat. No. 5,120,953, issued Jun. 9, 1992, Ohki,U.S. Pat. No. 5,122,653 issued Jun. 16, 1992, Webb, U.S. Pat. No.4,768,874 issued Sep. 6, 1988 and Pflibsen, U.S. Pat. No. 4,991,953issued Feb. 12, 1991. Such proposals have not provided a handheldinstrument which is readily usable by a surgeon in clinical examinationsfor imaging the epidermis and dermis, especially in vertical sections orin horizontal sections at desired depths below the surface of the skin.

SUMMARY OF THE INVENTION

Accordingly, it is the principal object of the present invention toprovide and improve clinical dermatological imaging system.

It is another object of the invention to provide an improved confocalimaging system which provides images of dermatological tissues andavoids the need for biopsies to detect the location of suchabnormalities as basal cell carcinomas and melanomas.

It is a still further object of the present invention to provide animproved confocal dermatological imaging system which does not requireionizing radiation and may use a laser beam.

It is a still further object of the present invention to provide animproved confocal imaging system which provides in vivo imaging ofdermatological tissue both at and below the skin and which may behandheld and which is capable of operating in various scattering media.

It is a still further object of the present invention to provide animproved confocal dermatological imaging system which may use a computerto generate images from data produced by the optics which providesconfocal imaging and to display or provide images for further evaluationor computer enhancement.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing objects, features and advantages of the invention willbecome more apparent from a reading of the following description inconnection with the accompanying drawings in which:

FIG. 1 is schematic diagram of a confocal imaging system embodying theinvention;

FIG. 1 a is a plan view of the head of the system shown in FIG. 1;

FIG. 2 is a block diagram of the system shown in FIG. 1, and especiallythe computer control and imaging system for acquisition and processingof the optical image;

FIG. 3 is a schematic diagram of the handheld confocal imaging system ofFIG. 2 in use.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 there is shown a system 10 for in vivo diagnosis ofdermatological tissues. The system 10 may be embodied in a handheld head32 as shown in FIG. 1 a and schematically in FIG. 3.

Referring more particularly to FIG. 1 there is shown a system 10 (orinstrument) which contains optics of the type which are used in opticaldata storage heads which are used in recording and reading opticaldisks. Light from a laser diode, contained in a laser and collimatorassembly 12, is collimated by a diffraction limited lens in the assembly12 and is incident at an oblique angle on a beam splitter assembly 14.Refraction at this oblique angle causes the elliptical laser diode beamto become circular in cross-section. The circular beam passes throughthe beam splitter assembly 14 and a quarter wave plate 16 and is focusedinto the tissue 22 via a contact window 20 (a glass window plate) spacedfrom the sample, specimen or tissue 22 being examined, preferably by anoptical contact liquid 21. In the event the sample is viscus or liquid,it may be located in a sample well (not shown).

The circular beam which passes through the beam splitter assembly 14 andthe quarter wave plate 16 is focused into the sample by a precisionfocusing lens 18, which suitably has a numerical aperture of 0.5 and afocal length of 4.3 millimeters. These dimensions and parameters areexemplary and demonstrate that the optical system 10 may be miniaturizedso as to be adapted to be handheld.

The quarter wave plate 16 converts the incident linear polarization fromthe laser in assembly 12 to circular polarization, i.e., the quarterwave plate is oriented 45° to the incident polarization. In other words,the beam from plate 16 is circularly polarized. The focusing lens 18 ismovable both in a direction along its optical axis and laterally asindicated by the arrows 24 and 25, respectively. Position mechanicalactuators 34 (FIG. 1 a) may be used for moving the lens 18, and therebycontrol position of the focus spot of beam in the sample. Theseactuators 34 may be similar to those used in optical disk systems. Thelens 18 may be mounted on a pair of such mechanical actuators. Theactuators 34 provide lateral and vertical scanning of the focused laserbeam in the tissue sample.

The focusing lens 18 also collects scattered light reflected from thesample. The amount of coherent light scattered back into the detectionsystem (which includes lens 18, plate 16 and assembly 14) depends uponlocal variations of the refractive index and the absorption in theimmediate neighborhood of the focus spot. This coherent light may bedefined as the component of the reflected light having a circularpolarization orthogonal to the polarization of the beam focused into thetissue sample. The scattered light is incident to plate 16 and then tobeam splitter assembly 14. The plate 18 converts the coherent componentof the scattered light into linear polarization, where beam splitterassembly 14 directs by reflection (or filters) the coherent lightcomponent of the scattered light at the beam splitting surface 15 in thebeam splitter assembly 14. The reflected light passes through a relaylens 26. The light from relay lens 26 may be reflected from a pair offold mirrors 28 (See also FIG. 1 a). These fold mirrors 28 may be partof the beam splitter assembly 14. The relay lens 26 may also be part ofthis assembly 14.

The scanned light from the focus spot is reflected from the fold mirrors28 to a pinhole photodetector assembly 30, which may also be consideredpart of the detection system. The fold mirrors 28 are used to make theinstrument more compact. A prism assembly may alternatively be used,which is part of the beam splitting assembly 14, and allows the samplesto be placed face down. This orientation allows gravity to assist inmaintaining the sample in a stable viewing position. Maintaining astable viewing position is also enhanced by the use of the window 20 asshown in FIG. 1.

A top view of the instrument is illustrated in FIG. 1 a. Typicaldimensions are given in FIG. 1 a to illustrate the compacted size of theconfocal imaging head 32. The elements in the head 32 may be located ona single board to provide unitized construction. The height of the headmay be approximately two inches from the base to the nominal focal pointof the focusing lens 18.

By scanning using the mechanical actuators 34 successive lines may bescanned at successive depths to provide images of vertical sections(i.e., along a vertical plane through the tissue sample). If desired theimages may be formed from horizontal sections (i.e., along a horizontalplane through the tissue sample) as the lines are scanned horizontally.By tilting the sample, sections at desired angles to the surface of thesample (i.e., along a tilted or non-perpendicular plane) may be formed,such sections may also be formed by moving the lens 18 via actuator 34as desired angles.

Referring to FIG. 2, there is shown a block diagram of the dataacquisition and analysis system which is part of the imaging system 10provided by the invention. The confocal head 32 is the head shown inFIGS. 1 and 1 a. The output 36 from the head 32 is the output from thepinhole detector assembly 30. This output 36 is the confocal detectorsignal. Signals are also provided from sensors 38, namely a lateralposition sensor and a vertical position sensor. These signals afteramplification and filtering are acquired by a analog to digitalconverter of a digital I/O board 40. This board 40 may also be on aboard with a circuit which provides a digital to analog channel to drivethe lateral motion actuator. The vertical scanning actuator is drivenfrom a signal derived from a conventional signal generator 42. The A toD, D to A and digital I/O board 40 is controlled and data is acquiredvia software in a personal computer 44, such as a Macintosh Quadra 950.Conventional software packages may be used for image analysis and fordriving a display 46, which is shown by way of example as a 1472 by 1088pixel display.

Referring to FIG. 3, there is shown the confocal imaging head 32contacted against the skin 48 of a subject specimen using a mineral oilas an optical index matching fluid, which is an optical contact liquid21 (FIG. 1) for reducing undesired reflections of light from the surfaceof the skin. The force against the skin 48 will be limited to thatrequired to press the skin against the contact window 20 of the head 32.A laser beam 50 which may be relatively low power (e.g., 6.3 milliwattsof optical power) is focused into the dermis of the specimen. The laseris operated at a wavelength capable of penetrating into the skin of thespecimen, thus the skin may be considered transparent to the laserwavelength (or in other words, the skin is permeable to electromagneticradiation of specified frequencies). The depth of focal point or spot 52is varied from the surface of the stratum corneum to a few millimetersbelow the surface of stratum corneum. The nominal beam spot size may be,for example, 2.5 micrometers, full width half maximum. The laser spot isscanned laterally across the skin, for example at a rate of 3 to 10 hz.Different laser wavelengths may be selectively used for differentresolution. Inasmuch as the energy delivered is proportional to theilluminating flux focused divided by the diameter of the spot, the scanlength and the scan rate or frequency, the amount of incident flux issufficiently low that damage to the specimen is avoided. The lightscattered by the tissue is collected and the lights coherent componentis re-imaged onto the pinhole aperture 54 of assembly 30, as shown inFIGS. 1 and 1 a. The pinhole 54 transmits the coherent light from thefocal region of the incident beam 53 to the detector 55 (of assembly 30)where it converts the light into an electrical signal. As the lens 18scans laterally, the electrical signal is acquired by the computer andstored. Each scan represents a one dimensional trace of the reflectivityand scattering cross section of the dermis at a given level below thesurface of the skin 48. A series of scans are made with the focal pointpositioned at progressively lower depths thereby providing a verticalcross section image of the skin which may be similar to a B-scanultrasound image. As stated earlier, these scans may also be horizontalto provide a horizontal cross-section, or at an angle to provide anangular cross-section of the skin.

From the foregoing description it will be apparent that there has beenprovided an embodiment of a confocal imaging system for dermatologicalpathology applications. Variations and modifications of the hereindescribed system and other applications for the invention willundoubtedly suggest themselves to those skilled in the art. Accordingly,the foregoing description should be taken as illustrative and not in alimiting sense.

1-26. (canceled)
 27. A microscopic imaging apparatus for imaging tissuesamples for pathological applications through an objective lens, saidapparatus comprising: an objective lens; a window having a surfacecapable of being pressed into a contact relationship with the surface ofsaid tissue sample in which said window is in optical communication withsaid objective lens; a housing capable of being handheld having at leastsaid objective lens and said window; and an illumination beam which isfocused by said objective lens through said window to said tissuesample, wherein said objective lens receives returned light from saidtissue sample representing a tissue section.
 28. The apparatus accordingto claim 27 further comprising a light source for said illuminationbeam.
 29. The apparatus according to claim 27 wherein said window istransparent to said illumination beam.
 30. The apparatus according toclaim 27 wherein said objective lens has a numerical aperture of lessthan one.
 31. The apparatus according to claim 27 wherein said housingis positionable to locate said window in direct contact with saidsurface of said tissue sample.
 32. The apparatus according to claim 27further comprising a detector and an aperture, in which said detectorreceives returned light via said aperture representing said tissuesection.
 33. The apparatus according to claim 27 wherein saidillumination beam is focused by said objective lens through said windowto locations on or within said tissue in accordance with said tissuesection.
 34. The apparatus according to claim 27 wherein said sectionrepresents one of a horizontal, vertical, or angled section on or withinsaid tissue.
 35. A microscopic imaging apparatus for imaging tissuesamples for pathological applications through an objective lens, saidapparatus comprising; an objective lens; a window having a surface thatis capable being in a direct pressure contacting relationship with thesurface of said tissue sample; a housing capable of being handheldhaving at least said window lens in optical communication with saidobjective lens; and an illumination beam which is focused by saidobjective lens through said window to said tissue sample, wherein saidobjective lens receives returned light from said tissue samplerepresenting a tissue section within or on the illuminated tissue samplein which said tissue section is in accordance with said focus in saidtissue sample.
 36. The apparatus according to claim 35 wherein saidsection is capable of being formed by said returned light along a regionof said focused illumination beam under the surface of said tissue. 37.The apparatus according to claim 35 further comprising a light sourcefor said illumination beam.
 38. The apparatus according to claim 35wherein said window is transparent to said illumination beam.
 39. Theapparatus according to claim 35 wherein said objective lens has anumerical aperture of less than one.
 40. The apparatus according toclaim 35 wherein said housing is positionable to locate said window indirect contact with said surface of said tissue sample.
 41. Theapparatus according to claim 35 wherein said section represents one of ahorizontal, vertical, or angled section on or within said tissue. 42.The apparatus according to claim 35 wherein said section is capable ofbeing formed by returned light along a region of said focus under thesurface of said tissue.
 43. A method for diagnosing a tumor in images ofone or more sections of in-vivo tissue comprising the steps of: placingsaid in-vivo tissue against a window having a surface in a pressurecontact relationship with the surface of said tissue; imaging the tissuethrough an objective lens to provide at least one image of a section ofthe tissue; and diagnosing in said image one or more cells of a tumor insaid tissue.
 44. The method according to claim 43 further comprising thestep of focusing an illumination beam with said objective lens throughsaid window to said tissue sample.
 45. The method according to claim 44further comprising the step of providing a light source for saidillumination beam.
 46. The method according to claim 43 wherein saidtumor represents one of carcinomas and melanomas.
 47. The methodaccording to claim 43 wherein said placing step further comprises thestep of pressing said surface of said window into said pressure contactrelationship with said surface of said tissue.
 48. The method accordingto claim 43 further comprising the step of visualizing the borders ofthe tumor in said image.
 49. The method according to claim 48 furthercomprising the step of excising the tumor cells from said tissue. 50.The method according to claim 43 wherein said imaging step furthercomprises the steps of: receiving return light from said tissuerepresenting a tissue section; and converting the returned light intoelectrical signals; and processing said electrical signals to provide adisplay of said image of said tissue section.